0703765v1 29 Mar 2007

Draft version February 4, 2008 Preprint typeset using LATEX style emulateapj v. 10/09/06

X-RAY, UV, AND OPTICAL OBSERVATIONS OF SUPERNOVA 2006bp WITH SWIFT: DETECTION OF EARLY X-RAY EMISSION S. Immler1,2 , P. J. Brown3 , P. Milne4 , L. Dessart4 , P. A. Mazzali5,6 , W. Landsman1 , N. Gehrels7 , R. Petre1 , D. N. Burrows3 , J. A. Nousek3 , R. A. Chevalier8 , C. L. Williams1 , M. Koss1 , C. J. Stockdale9 , M. T. Kelley9 , K. W. Weiler10 , S. T. Holland1,2 , E. Pian5 , P. W. A. Roming3 , D. Pooley11,12 , K. Nomoto13 , J. Greiner14 , S. Campana15 , and A. M. Soderberg16

arXiv:astro-ph/0703765v1 29 Mar 2007

Draft version February 4, 2008

ABSTRACT We present results on the X-ray and optical/UV emission from the type IIP supernova (SN) 2006bp and the interaction of the SN shock with its environment, obtained with the X-Ray Telescope (XRT) and UV/Optical Telescope (UVOT) on-board the Swift observatory. SN 2006bp is detected in X-rays at a 4.5σ level of significance in the merged XRT data from days 1 to 12 after the explosion. If the (0.2–10 keV band) X-ray luminosity of L0.2−10 = (1.8 ± 0.4) × 1039 ergs s−1 is caused by interaction of the SN shock with circumstellar material (CSM), deposited by a stellar wind from the progenitor’s companion star, a mass-loss rate of M˙ ≈ 1 × 10−5 M⊙ yr−1 (vw /10 km s−1 ) is inferred. The mass-loss rate is consistent with the non-detection in the radio with the VLA on days 2, 9, and 11 after the explosion and characteristic of a red supergiant progenitor with a mass around ≈ 12–15 M⊙ prior to the explosion. The Swift data further show a fading of the X-ray emission starting around day 12 after the explosion. In combination with a follow-up XMM-Newton observation obtained on day 21 after the explosion, an X-ray rate of decline Lx ∝ t−n with index n = 1.2 ± 0.6 is inferred. Since no other SN has been detected in X-rays prior to the optical peak and since type IIP SNe have an extended ’plateau’ phase in the optical, we discuss the scenario that the X-rays might be due to inverse Compton scattering of photospheric optical photons off relativistic electrons produced in circumstellar shocks. However, due to the high required value of the Lorentz factor (≈ 10–100), inconsistent with the ejecta velocity inferred from optical line widths, we conclude that Inverse Compton scatterring is an unlikely explanation for the observed X-ray emission. The fast evolution of the optical/ultraviolet (1900–5500˚ A) spectral energy distribution and the spectral changes observed with Swift reveal the onset of metal line-blanketing and cooling of the expanding photosphere during the first few weeks after the outburst. Subject headings: stars: supernovae: individual (SN 2006bp) — stars: circumstellar matter — X-rays: general — X-rays: individual (SN 2006bp) — X-rays: ISM — ultraviolet: ISM

Electronic address: [email protected] 1 Astrophysics Science Division, X-Ray Astrophysical Laboratory, Code 662, NASA Goddard Space Flight Center, Greenbelt, MD 20771 2 Universities Space Research Association, 10211 Wincopin Circle, Columbia, MD 21044 3 Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 4 Steward Observatory, 933 North Cherry Avenue, RM N204 Tucson, AZ 85721 5 INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy 6 Max-Planck-Institut f¨ ur Astrophysik, Karl-Schwarzschild Strasse 1, 85741 Garching, Germany 7 Astrophysics Science Division, Astroparticle Physics Laboratory, Code 661, NASA Goddard Space Flight Center, Greenbelt, MD 20771 8 Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 9 Department of Physics, Marquette University, P.O. Box 1881, Milwaukee, WI 53201-1881 10 Naval Research Laboratory, Code 7210, Washington, DC 20375-5320 11 Astronomy Department, University of California at Berkeley, 601 Campbell Hall, Berkeley, CA 9472 12 Chandra Fellow 13 Department of Astronomy, School of Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan 14 Max-Planck-Institut f¨ ur extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany 15 INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate, Italy

1. INTRODUCTION

SN 2006bp was discovered on April 9.6, 2006, with an apparent magnitude of 16.7 in unfiltered 20-s CCD exposures using a 0.60-m f/5.7 reflector (Nakano & Itagaki 2006). Subsequent observations by Itagaki showed that the SN brightened rapidly between April 9.6 and 9.8 UT. The non-detection in unfiltered ROTSE-IIIb observations on April 9.15 UT (> 16.9 mag; Quimby et al. 2006) give a likely explosion date of April 9, 2006. Based on the optical/UV colors (Immler, Brown & Milne 2006) observed with Swift and the detection of hydrogen and helium lines in ground-based optical spectra (Quimby et al. 2006), SN 2006bp was classified as a core-collapse type II SN. The optical/UV lightcurve established by Swift (this work) shows that SN 2006bp belongs to the class of type IIP SNe which are characterized by a prolonged ’plateau’ period of sustained optical flux (see Sec. 3.1). This plateau phase results from recombination in the massive hydrogen envelopes (> ∼ 2M⊙ H mass) of the progenitors. Most massive stars (≈ 8–25 M⊙ ) become type II SNe, approximately 2/3 of which are type IIP 16 Division of Physics, Mathematics, and Astronomy, California Institute of Technology, MS 105-24, Pasadena, CA 91125

2

Immler et al.

(Heger et al. 2003) depending on the mass and metallicity. Due to the large masses of the progenitor stars and high abundance of type IIP SNe, they play a primary role in the formation of neutron stars. Such massive progenitor stars have strong stellar winds which can deposit significant amounts of material in their environments. As the outgoing SN shock runs through the CSM deposited by the stellar wind, large amounts of X-ray emission and radio synchrotron emission can be produced. Four of the 26 SNe detected in X-rays to date17 are type IIP: SNe 1999em, 1999gi, 2002hh, and 2004dj (see Tables 1, 2 and references in Chevalier et al. 2006). Mass-loss rate estimates from the X-ray and radio observations are between a few ×10−6 to 10−5 M⊙ yr−1 (vw /10 km s−1 ), where vw is the pre-SN stellar wind velocity. In this paper we present the earliest observation and detection of a SN in X-rays to date, starting one day after the explosion. In addition to the Swift X-ray and a follow-up XMM-Newton X-ray observation, we discuss the broad-band spectral energy distribution during the early evolution (days to weeks) of SN 2006bp, as well as multi-epoch UV spectra obtained with Swift. 2. OBSERVATIONS 2.1. Swift UVOT Optical/UV Observations

The Ultraviolet/Optical Telescope (UVOT; Roming et al. 2005) and X-Ray Telescope (XRT, Burrows et al. 2005) on-board the Swift Observatory (Gehrels et al. 2004) began observing SN 2006bp on April 10.54 UT. The HEASOFT18 (version 6.1.1) and Swift Software (version 2.5, build 19) tools and latest calibration products were used to analyze the data. The SN was detected with the UVOT at R.A. = 11h53m55s.70, Decl. = +52o 21′ 10.′′ 4 (equinox 2000.0), with peak magnitudes of V = 15.1, B = 15.4, U = 14.5, U V W 1 [216–286 nm FWHM] = 14.7, U V M 2 [192– 242 nm] = 15.1, and U V W 2 [170–226 nm] = 14.8. Statistical and systematic errors are 0.1 mag each. Based on the UVOT photometry and V − B and B − U colors, the SN was classified as a young type II event (Immler, Brown & Milne 2006). The classification was confirmed by Hobby-Eberly Telescope (HET) spectra taken on day 2, showing a blue continuum and a narrow absorption line at 592 nm, consistent with Na I in the host galaxy NGC 3953 rest frame (z = 0.00351, Verheijen & Sancisi 2001), a narrow emission line consistent with rest-frame Hα, a broad absorption line around 627 nm, and a narrow but slightly broadened emission line at 583 nm (Quimby et al. 2006). Thirty-five individual exposures were obtained between April 10.54 UT and May 30.45 UT (see Table 1 for an observation log). Assuming an explosion date of April 9, the observations correspond to days 1–51 after the explosion. Swift optical, UV, and X-ray images of SN 2006bp and its host galaxy NGC 3953 (Hubble type SBbc; NED) are shown in Fig. 1. The UVOT 6-filter lightcurve of SN 2006bp is given in Fig. 2. 2.2. Swift Grism Observations

TABLE 1 Swift Observations of 2006bp Sequence (1)

Date [UT] (2)

XRT Exp [s] (3)

UVOT Exp [s] (4)

30390001 2006-04-10 12:47:26 4333 4917 30390003 2006-04-11 03:22:00 4323 4301 30390004 2006-04-12 08:19:01 3157 2770 30390005 2006-04-12 03:30:00 1705 1684 30390006 2006-04-13 03:37:00 6906 6660 30390007 2006-04-14 08:38:01 748 746 30390008 2006-04-14 16:39:01 868 899 30390009 2006-04-14 08:34:01 156 155 30390010 2006-04-14 16:36:01 4 4 30390011 2006-04-15 07:06:01 3373 3296 30390012 2006-04-15 18:22:01 1572 1544 30390013 2006-04-16 05:36:00 260 260 30390014 2006-04-16 18:29:00 80 81 30390015 2006-04-16 05:39:01 3013 2995 30390016 2006-04-16 18:30:02 1537 1526 30390017 2006-04-17 04:04:01 3666 3494 30390018 2006-04-17 18:35:01 1639 1612 30390019 2006-04-18 07:23:00 61 57 30390020 2006-04-18 07:27:01 2609 2935 30390021 2006-04-20 14:00:01 3174 3118 30390022 2006-04-21 06:04:01 363 364 30390023 2006-04-21 06:09:01 2741 2743 30390024 2006-04-22 02:57:00 2801 2749 30390025 2006-04-23 03:03:01 742 743 30390026 2006-04-23 03:07:01 5248 5221 30390027 2006-04-24 01:32:01 2999 2733 30390028 2006-04-26 01:43:00 1782 1642 30390029 2006-04-28 00:50:01 2829 2693 30390030 2006-05-01 10:14:01 974 965 30390031 2006-05-01 11:50:01 3793 3914 30390032 2006-05-04 04:06:01 2542 2450 30390034 2006-05-10 00:21:40 884 873 30390036 2006-05-22 12:17:00 622 863 30390037 2006-05-22 12:34:01 633 976 30390038 2006-05-30 08:32:01 5242 5143 Note. — (1) Swift sequence number; (2) Date in units of Universal Time (UT); (3) X-Ray Telescope (XRT) exposure time in units of s; (4) Ultraviolet/Optical Telescope (UVOT) exposure time in units of s.

The UVOT includes two grisms for obtaining spectra in the UV and visible bands. The UV grism has a nominal wavelength range of 1800—2900 ˚ A, while the V grism has a wavelength range of 2800–5200 ˚ A. The UV grism also records spectra in the 2900–4900 ˚ A range, but at half the sensitivity of the V grism, and with the possibility of contamination by second order overlap. We obtained six UV grism spectra and one V grism spectrum of SN 2006bp. The four earlier grism observations had moderate to severe contamination from the host galaxy and bright stars in the field and are not used in this study. The successful grism observations are shown in Fig. 3. A log of the observations is given in Table 2. 2.3. Swift XRT Observations

The Swift XRT observations were obtained simultaneously with the UVOT and grism observations. X-ray counts were extracted from a circular region with an aperture of 10 pixel (24′′ ) radius centered at the position of the SN. The background was extracted locally from a source-free region of radius of 1′ to account for detector and sky background, and for a low level of residual diffuse emission from the host galaxy.

17 see http://lheawww.gsfc.nasa.gov/users/immler/supernovae list.html for a complete list of X-ray SNe and references 18 http://heasarc.gsfc.nasa.gov/docs/software/lheasoft/

2.4. XMM-Newton Observation

X-Ray, UV, and Optical Observations of SN 2006bp

3

Fig. 1.— Swift optical, UV, and X-ray image of SN 2006bp and its host galaxy NGC 3953. Left-hand panel: Swift optical image, constructed from the UVOT V (750 s exposure time; red), B (1,966 s; green) and U (1,123 s; blue) filters obtained from 34 co-added images taken between 2006-04-10.54 UT and 2006-05-30.45 UT. The optical images are slightly smoothed with a Gaussian filter of 1.5 pixel (FWHM). The position of SN 2006bp is indicated by a white circle of 10 arcsec radius. The size of the image is 6.5 arcmin × 6.5 arcmin. Middle panel: The UV image was constructed from the co-added UVOT U V W 1 (750 s exposure time; red), U V M 2 (1,966 s; green) and U V W 2 (1,123 s; blue) filters obtained between 2006-04-10.54 UT and 2006-05-30.45 UT. The UV images are slightly smoothed with a Gaussian filter of 1.5 pixel (FWHM). Same scale as the left-hand panel. Right-hand panel: The (0.2–10 keV) X-ray image was constructed from the merged 41.4 ks XRT data and is adaptively smoothed to archive a S/N in the range 2.5–4. Contour levels are 0.3, 0.6, 0.9, 1.5, 3, 6, 12, and 20 counts pixel−1 . Same scale as the optical and UV images. 14

t [d] (1)

Sequence

Mode

(2)

(3)

Tstart [UT] (4)

Exp [s] (5)

Nexp (6)

9 00030390020 UV 2006-04-18T07:30:28 2,431 2 12 00030390023 V 2006-04-21T06:10:22 2,688 2 14 00030390026 UV 2006-04-23T03:10:13 3252 4 Note. — (1) Days after the explosion of SN 2006bp (April 9, 2006); (2) Swift sequence number; (3) UVOT grism mode; (4) Exposure start time in unites of UT; (5) Exposure time in units of s; (6) Number of individual exposures.

An XMM-Newton European Photon Imaging Camera (EPIC) Director’s Discretionary Time (DDT) observation was performed on April 30.39 UT (PI Immler, obs-id 0311791401), corresponding to day 21 after the explosion. SAS19 (version 7.0.0), FTOOLS20 (version 6.1.1), and the latest XMM-Newton calibration products were used to analyze the XMM-Newton data. Inspection of the EPIC PN and MOS data for periods with a high particle background showed no contamination of the data, which resulted in clean exposure times of 21.2 ks for the PN and 22.9 ks for each of the two MOS instruments. 2.5. VLA Radio Observation Radio observations were performed with the VLA21 at three epochs (days 2, 9, and 11) with a search for radio emission conducted within a radius of 10′′ of the optical position (Nakano & Itagaki, 2006) using AIPS22 . Upper limits (3σ) to any radio flux density were established at < 0.414 mJy on 2006 April 11.97 UT (spectral luminosity < 1.1 × 1026 ergs−1 Hz−1 for an assumed dis19

http://xmm.vilspa.esa.es/sas/ http://heasarc.gsfc.nasa.gov/docs/software.html 21 The VLA telescope of the National Radio Astronomy Observatory is operated by Associated Universities, Inc. under a cooperative agreement with the National Science Foundation 22 http://www.aoc.nrao.edu/aips/ 20

Vega Magnitude + constant

TABLE 2 UVOT Grism Observations of 2006bp

16

18

20

22

V B U + 1.5 UVW1 + 1.5 UVM2 + 2 UVW2 + 3 840

850

860

870

880

Julian Date (2453000+)

Fig. 2.— Swift UVOT lightcurve of SN 2006bp obtained in all six filters. The U , U V W 1, U V M 2, and U V W 2 lightcurves were shifted down vertically by 1.5, 1.5, 2, and 3 mag, respectively, to avoid overlap.

tance of 14.9 Mpc) at 22.46 GHz (wavelength 1.3 cm) and < 0.281 mJy at 8.460 GHz (wavelength 3.5 cm); on 2006 April 18.27 at < 0.498 mJy at 14.94 GHz (wavelength 2.0 cm); and on 2006 April 20.16 at < 0.276 mJy at 22.46 GHz and < 0.143 mJy at 8.460 GHz (Kelley et al. 2006). Although only uncertain mass-loss rate estimates can be obtained from radio non-detections, under standard assumptions (vw = 10 km s−1 ; vs = 104 km s−1 ; TCSM = 3–10 × 104 K; m = 1.0; see, e.g. Weiler et al. 2002 and Lundqvist & Fransson 1988), the upper limit to the radio-determined pre-SN mass-loss rate is estimated to be 10−6 to 10−5 M⊙ yr−1 . 3. RESULTS 3.1. Swift UVOT Optical/UV Observations The Swift V -band UVOT observations show that the SN reached its maximum brightness around day seven after the estimated time of explosion, faded slightly over

Immler et al.

the next few days and subsequently reached a plateau phase characteristic for type IIP SNe (see Fig. 2). At increasingly shorter wavelengths, the SN shows an earlier maximum and steeper rates of decline. In the roughly linear period 5–15 days after the explosion, the decay slopes are approximately 0.21, 0.25, 0.16, 0.06, 0.02, and 0.01 mags/day in the U V W 2, U V M 2, U V W 1, U , B, and V bands, respectively.

3.2. Swift and XMM-Newton X-ray Observations

An X-ray source is detected in the merged 41.4 ks Swift XRT observations obtained between days 1–12 after the explosion at R.A. = 11h53m56s.1, Decl. = +52o 21′ 11.′′ 1 (positional error 3.′′ 5), consistent with the optical position of the SN. The aperture-, backgroundand vignetting-corrected net count rate is (1.3 ± 0.3) × 10−3 cts s−1 (0.2–10 keV band). Two additional X-ray sources are detected within the D25 diameter of the host galaxy, as well as an X-ray source associated with the nucleus of the host galaxy (see Fig. 1). The chance probability of any of the three X-ray sources being within a radius of 3.′′ 5 at the position of SN 2006bp is estimated to be 1.5 × 10−3 . Adopting a thermal plasma spectrum with a temperature of kT = 10 keV (see Fransson, Lundqvist & Chevalier 1996 and therein) and assuming a Galactic foreground column density with no intrinsic absorption (NH = 1.58 × 1020 cm−2 ; Dickey & Lockman 1990) gives a 0.2–10 keV X-ray band unabsorbed flux and luminosity of f0.2−10 = (6.8 ± 1.6) × 10−14 ergs cm−2 s−1 and L0.2−10 = (1.8 ± 0.4) × 1039 ergs s−1 , respectively, for a distance of 14.9 Mpc (z = 0.00351, Verheijen & Sancisi 2001; H0 = 71 km s−1 Mpc−1 , ΩΛ = 2/3, Ωm = 1/3). The SN is not detected in merged 23.1 ks XRT data obtained between days 12–31 after the explosion. The (3σ) upper limit to the X-ray count rate is < 8.1×10−4 cts s−1 (0.2–10 keV), corresponding to an unabsorbed flux and luminosity of f0.2−10 < 4 × 10−14 ergs cm−2 s−1 and L0.2−10 < 1 × 1039 ergs s−1 . In order to probe the evolution of the X-ray emission in more detail, we subdivided the data taken before day 12 into two observations with similar exposure times of ≈ 20 ks each (see Table 3). Within the errors of the photon statistics, no significant decline is observed over the first 12 days after the explosion (see Fig. 4). To follow the X-ray rate of decline over a longer period, an XMM-Newton observation was obtained on day 21 after the explosion. The SN is detected at a 4.9σ level of confidence, with an EPIC PN net count rate of (3.0 ± 0.6) × 10−3 cts s−1 (0.2–10 keV band), corresponding to an unabsorbed flux and luminosity of f0.2−10 = (1.4±0.3)×10−14 ergs cm−2 s−1 and L0.2−10 = (3.8 ± 0.8) × 1038 ergs s−1 . A best fit X-ray rate of decline of Lx ∝ t−n with index n = 1.2 ± 0.6 is obtained using the Swift XRT and XMM-Newton detections. The X-ray lightcurve of SN 2006bp is given in Fig. 4. Due to the limited photon statistics of the Swift XRT and XMM-Newton EPIC data, no detailed spectral fitting is possible. 4. DISCUSSION 4.1. Ultraviolet Emission

8 Flux (10−15 erg cm−2 s−1 Å−1)

4

6

4

2 00030390020 Apr 18 00030390023 Apr 21 00030390023 Apr 23 0 2500

3000

3500 4000 Wavelength (Å)

4500

5000

Fig. 3.— Swift UV grism observations of SN 2006bp obtained on April 18, 21, and 23, 2006, corresponding to days 9, 12, and 14 after the explosion.

UV emission from SNe explosions can arise from different physical processes. The first photon signature from a core-collapse SN event is thought to be associated with shock break-out, which should manifest itself in a burst of light peaking in the X-rays and the far-UV (Ensman & Burrows 1992; Blinnikov & Bartunov 1993; Blinnikov et al. 1998, 2000; Li 2006). The exact duration of this emission can be from hours to days, depending on the progenitor structure. Fast expansion of the ejecta and efficient radiative cooling at its ’photosphere’ make this epoch short lived and therefore difficult to observe. At such early times, the object is not bright in the optical, and is thus usually still undetected. A SN is usually discovered when it becomes bright in the optical, but at this time the photosphere has cooled too much for Xray emission. Observational evidence for a shock breakout was provided by Swift observations of the GammaRay Burst (GRB) related to SN 2006aj (Campana et al. 2006), although this was probably mediated by a cocoon of material lost by the star before it collapsed. UV emission has also been observed at early times (. 2 weeks) in the photospheric phase of SN ejecta, emanating from the progenitor envelope layers that transition from thick to thin over time when the ejecta are still very hot (e.g. Mazzali 2000). The UV emission is typically strongest during early times (as in the spectrum of SN 1987A on day one; Pun et al. 1995) and fades substantially over the course of a few days (weak UV emission has been detected in an HST observation of SN 1993J, 18 days after the explosion; Jeffery et al. 1994; Baron et al. 1994). At later times (> ∼weeks), UV emission is in general associated with the interaction of the ejecta with the CSM (Fransson et al. 1987, 2002; Pun et al. 2002). The UV is therefore a very sensitive spectral probe of the fast changing conditions in the SN expanding photosphere during the earliest phases. The first observation of SN 2006bp shows a spectral energy distribution (SED) peak in the UV, rather than the optical (Fig. 5), which supports that the SN was detection very early. Thirty-five observations finely sample the lightcurve over 51 days after discovery, revealing a flux variation in the UV by two orders of magnitude. The redward shift of the SED stems from cooling of the photosphere. There is a direct effect in the reduction of the equivalent blackbody (or effective/electron) temper-

X-Ray, UV, and Optical Observations of SN 2006bp

5

TABLE 3 X-Ray Observations of 2006bp Day after Explosion (1)

Instrument (2)

Exposure [ks] (3)

S/N [σ] (4)

Rate [10−3 ] (5)

fx [10−14 ] (6)

Lx [1039 ] (7)

1–5 Swift XRT 20.0 4.4 1.31 ± 0.30 6.94 ± 1.58 1.84 ± 0.42 6–12 Swift XRT 21.5 4.4 1.25 ± 0.29 6.58 ± 1.52 1.75 ± 0.40 13–31 Swift XRT 23.1 4 days (SN 2002ap) and a few weeks. The bulk of all X-ray observations took place weeks to months after the explosions. Therefore, if SN 2006bp is more typical for a larger sample of corecollapse SNe, then the early production of X-rays would have been missed in each of the previous cases. The response time of our ongoing Swift observing program to study the prompt emission of SNe across the optical, UV, and X-rays is currently only limited by the time lag between the explosion of a SN and its discovery at optical wavelengths and timely alert by the community.

1e-14

1e-15 2006-04-10 2006-04-11 2006-04-13 2006-04-15 2006-04-17 2006-04-22 2006-05-01

1e-16

2000

3000

4000

7

5000

Wavelength (Angstroms) Fig. 5.— Evolution of the spectral energy distribution (SED) of SN 2006bp in the optical/UV wavelength band. The SED was produced from near-simultaneous UVOT observations in all six filters obtained between days 1 and 26 after the explosion (from top to bottom).

Currently, Swift is the only telescope capable of revealing the fast changes in the UV flux from SN explosions, offering sensitive constraints on the ionization state in the continuum and line formation region of the ejecta, the sources of metal line-blanketing. By extending the spectral coverage, this provides stronger constraints on the reddening, and complementary information, to what can be deduced from optical observations alone. While there is ample evidence for diversity in type II SN optical spectra, Swift observations can be used to address the existence of a corresponding diversity in the UV range. The detection of SN 2006bp in X-rays at such an early epoch, as well as the detection of its fast optical/UV spectral evolution was made possible by the quick response of the Swift satellite, and underlines the need for rapid observations of SNe in the UV and in X-rays. It

We gratefully acknowledge support provided by STScI grant HST-GO-10182.75-A (P.A.M), NASA Chandra Postdoctoral Fellowship grant PF4-50035 (D.P.), and NSF grant AST-0307366 (R.A.C). L.D acknowledges support for this work from the Scientific Discovery through Advanced Computing (SciDAC) program of the DOE, grant DE-FC02-01ER41184 and from the NSF under grant AST-0504947. K.W.W. thanks the Office of Naval Research for the 6.1 funding supporting this research. C.J.S. is a Cottrell Scholar of Research Corporation and work on this project has been supported by the NASA Wisconsin Space Grant Consortium. This work is sponsored at The Pennsylvania State University by NASA contract NAS5-00136. We wish to thank N. Schartel and the XMM-Newton SOC for approving and scheduling a XMM-Newton DDT observation. The research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

REFERENCES Baron, E., Hauschildt, P. H., & Branch, D. 1994, ApJ 426, 334 Bjornsson, C.-I., & Fransson, C. 2004, ApJ 606, 823 Blinnikov, S., & Bartunov, O. S. 1993, A&A 273, 106 Blinnikov, S., Eastman, R. G., Bartunov, O. S., Popolitov, V. A., & Woosley, S. E. 1998, ApJ 496, 454 Blinnikov, S., Lundqvist, P., Bartunov, O. S., Nomoto, K., & Iwamoto, K. 2000, ApJ 532, 1132 Burrows, D. N. et al. 2005, Space Science Reviews 120, 165 Campana, S. et al. 2006, Nature 442, 1008 Cash, W. 1979, ApJ 228, 939 Chevalier, R. A. 1982, ApJ 259, 302 Chevalier, R. A. & Fransson, C. 2003, in Supernovae and GammaRay Bursters (ed K. Weiler), Lecture Notes in Physics, 598, 171 Chevalier, R. A., Fransson, C., Nymark, T. K. 2006, ApJ 641, 1029 Chieffi, A., Dom´ınguez, I., H¨ oflich, P., Limongi, M., Straniero, O. 2003, MNRAS 345, 111 Dessart, L., & Hillier, D. J. 2006, A&A 447, 691 Dessart, L., & Hillier, D. J. 2005, A&A 437, 667 Dickey, J. M., Lockman, F. J. 1990, ARA&A 28, 215 Eastman, R. G., & Kirshner, R. P. 1989, ApJ 347, 771 Ensman, L., & Burrows, A. 1992, ApJ 393, 742 Fransson, C., Grewing, M., Cassatella, A., Wamsteker, W., & Panagia, N. 1987, A&A 177, L33 Fransson, C., Lundqvist, P., Chevalier, R. A. 1996, ApJ 461, 993 Fransson, C., et al. 2002, ApJ 572, 350 Gehrels, N. et al. 2004, ApJ 611, 1005 Heger, A., Fryer, C. L., Woosley, S. E., Langer, N., Hartman, D. H. 2003, ApJ 591, 288 Immler, S., Wilson, A. S., Terashima, Y. 2002, ApJ 573, L27

Immler, S., Lewin, W. 2003, in Supernovae and Gamma-Ray Bursters (ed K. Weiler), Lecture Notes in Physics, 598, 91 Immler, S., Brown, P., Milne, P. 2006, ATel 793, 1 Immler, S. et al. 2006, ApJ 648, L119 Jeffery, D. J., et al. 1994, ApJ 421, L27 Kelley, M. T., Stockdale, C. J., Sramek, R. A., Weiler, K. W., Immler, S., Panagia, N., van Dyk, S. D. 2006, CBET 495, 1 Lentz, E. J., Baron, E., Branch, D., Hauschildt, P. H., & Nugent, P. E. 2000, ApJ 530, 966 Li, Li-Xin, 2006, accepted for publication by MNRAS (astro-ph/0605387) Lundqvist, P., & Fransson, C. 1988, A&A 192, 221 Mazzali, P. A. 2000, A&A 363, 705 Mazzali, P. A., & Chugai, N. N. 1995, A&A 303, 118 Mazzali, P. A., & Lucy, L. B. 1993, A&A 279, 447 McCray, R. 1993, ARA&A 31, 175 Nakamo, S., Itagaki, K. 2006, CBET 470 1 Park, S., et al. 2006, ApJ 646, 1001 Pian, E., et al. 2000, ApJ 536, 778 Pun, C. S. J., et al. 2002, ApJ 572, 906 Pun, C. S. J., et al. 1995, ApJ 99, 223 Quimby, R., Brown, P., Caldwell, J., Rostopchin, S. 2006, CBET 471, 1 Roming, P. W. A., et al. 2005, Space Science Reviews 120, 95 Verheijen, M. A. W., Sancisi, R. 2001, ApJ 370, 765 Weiler, K. W., Panagia, N., Montes, M. J., Sramek, R. A. 2002, ARA&A 40, 387